Tool for severing and milling away a section of casing in the bore of a well



Filed Sept. 28, 1951 Julia TOOL FOR SEVENING AND MILLING AWAY A SECTIONOF CASING IN THE BORE OF A WELL 3 Sheets-Sheet 1 ZNVENTOR HARRY C.TRIMBLE ALBERT E. WOELFEL ATTORNEY may El, 1955 c, TRIMBLE ET AL2,709,499

TOOL FOR SEVERING AND MILLING AWAY A SECTION OF CASING IN THE BORE OF AWELL Filed Sept. 28, 1951 3 Sheets-Sheet 2 INVENTOR HARRY C TRIMBLEALBERT E. WOELFEL.

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TOOL FOR SEVERIN ND MIL WAY A SECTION OF CASING THE B0 A WELL 3Sheets-Sheet 3 Filed Sept. 28, 1951 IN VENTOR HARRY CTRIMBLE ALBERT E.WCJELFEL.

ATTORNEY TUUL FUR SEVERHNG AND MILLING AWAY A SIECTTUN @F @ASllNG IN THEBGRE OF A WELL Harry (I. Trimbie, New @rleans, La., and Albert E.Woeitci, Houston, Tex., assignors to A-1 Bit & Tool Company,incorporated, Houston, Tex., a corporation or Texas ApplicationSeptember 23, 1951, Serial No. 248,7il2 14 Claims. (Cl. loft-0.8)

This invention relates to a casing mill, and more particularly to animproved milling tool for severing and milling away a section of thecasing in the bore of a well.

In the production and operation of wells, and particularly oil wells, itis frequently necessary to remove a portion of the casing in the well atsome predetermined location for various purposes, such as side trackingoperations or to expose a producing stratum. Thus, it may be desirableto remove a section of the casing to allow a whipstock to be set in anopen window, or to expose a sand stratum or other potentially productiveformation which has been previously cased 05.

Such operations frequently must be conducted at great depths in thewell, which depth presents serious problems in both the character or"the tools employed and the manner in which the operation is carried out.These problems arise principally because of the great weight of theoperating string by which milling tools usually are operated and alsobecause of frequent deviation of the bore of the well from the vertical.

Milling tools generally in use consist of a cutter head which isconnectable to the lower end of a drill string for rotation thereby andhas a plurality of cutters pivotally mounted for radial outward movementinto cutting engagement with the casing. Means within the cutter headand operable by pressure of drilling fluid in the string are normallyemployed to move the cutters outwardly against the casing. After thecutters have been projected, the drill string is rotated to operate thecutters against the inner wall of the casing to sever the same, afterwhich severance the cutters move further outwardly through the cut intomilling engagement with an end of the severed casing. Continued rotationof the drill string combined with axial movement thereof then isemployed to mill away a section of the casing.

The above described operation presents a serious prob lem in controllingthe load on the cutters, both because of the tremendous weight of thedrill string and the stretch therein when the milling operation isconducted at a great depth in the well. it can easily be seen that ifthe entire weight of the drill string is supported on the cutters, thelatter are apt to be severely damaged by breakage or to wear too rapidlyfor practical purposes. In other words, accurate control of the pressureof the engagement of the cutters with the casing is extremely difiicultfrom the mouth of the well.

in addition to the aforementioned problem arising with conventionalcasing mills, there is still another problem in maintaining all of thecutter blades in equally efifective cutting engagement with the end ofthe casing. Although conventional casing mills are constructed withutmost precision, because of uneven wear of the several cutters andvarious dimensional and material imperfections in the construction ofmilling tools, the cutting edges of the cutters of casing millsheretofore in use cannot be maintained in a single transverse plane. Theconsequent resuit is that usually only one, or less than all, of thenumerous cutters are eflective at any one time so that the full d StatesPatent ice benefit from the use of a plurality of cutters is notobtained.

Hence, it is an object of this invention to provide a casing mill of t.e type under consideration in which axial movement of the cutter headduring a milling operation may be controlled without axial movement ofthe drill string.

it is another object of this invention to provide an improved casingmill in which the cutter head is mounted for axial movement on the endof a drill string, and such axial movement controlled at the mouth ofthe well by fluid pressure.

It is still another object of this invention to provide an improvedcasing mill in which the cutter head is mounted for axial movement onthe end of the drill string, and such axial movement controlled by fluidpressure at the mouth of the well, but in which the cutter head islocked against such axial movement until the cutters have severed thecasing and moved into milling engagement with a severed end thereof.

it is still another object of this invention to provide an improvedcasing mill in which the cutters are individually maintained in millingengagement with the severed end of a casing so that all of the cuttersare equally effective at all times, with a consequent increase inmilling rate.

it is a further object of this invention to provide an improved casingmill of simple and, consequently, relatively inexpensive constructionfor accomplishing the above objects.

Other objects and advantages of this invention will be apparent from thefollowing description and accompanying drawings, in which:

Figure l is an elevational view of a casing mill embodying thisinvention showing the mill in position in a section of a cased borehole.

Figures 2A and 2B are enlarged fragmentary elevational sectional viewsof upper and lower portions, respectively, of the milling tool shown inFigure 1. The section through. the cutter head is taken, for purposes ofillustration, on line 2B-2B of Figure 7.

Figure 3 is an enlarged fragmentary view of a portion of the millingtool shown in Figure 2B, with the cutters shown in the position ofmilling engagement with the severed end of a casing. The section throughthe cutter head is taken, for purposes of illustration, on line 3-3 ofFigure 8.

Figures 4 and 5 are sectional views taken on the correspondinglynumbered section lines of Figure 2A.

Figures 6 and 7 are enlarged sectional views taken on the correspondingsection lines of Figure 2B.

Figure 8 is a sectional view taken on line 8--S of Figure 3.

Referring now to the drawings, the improved casing mill embodying thisinvention comprises an elongated tubular mandrel 1t) adapted to beconnected to, supported from, and to receive pressure fluid from thelower end of a drill string 12 by a threaded coupling member 14.Tclescoped over the mandrel 10 is a sleeve 16 having, for the majorportion of its length, an inner diameter greater than the outer diameterof the mandrel. The upper portion of the sleeve 16, however, is extendedinwardly into sliding engagement with the mandrel l6 and provided withlongitudinal grooves 13 which receive corresponding longitudinal ribs 20on, and extending substantially the full length of, the mandrel to forma splined joint. By means of this construction it will be seen that thesleeve 16 is rotatable with the mandrel 10, but axially movable withrespect thereto. Adjacent its lower end, the mandrel id is provided witha piston-like annular enlargement 22 (see Figure 28) having outercircumferential grooves in which O-ring packing 24 is disposed forsealing engagement with the inner wail of the sleeve 316i Thus, the

splined joint is sealed, and relative axial movement between the sleeve16 and the mandrel permitted, without hindrance from fluid in thechamber 26 therebetween, by lateral vent ports 28 in the sleeveimmediately below the mandrel-engaging upper portion of the latter.

A threaded coupling 30 is secured to the lower end of the sleeve 16 andsupports a cutter head 32 in spaced relation below the lower end of themandrel 10. The lower end of the mandrel 10 projects into the bore 54 ofthe coupling 30 and, adjacent its lower end, is provided with acircumferential series, three as shown in the drawings, of circularradial apertures 36. A corresponding number of radial apertures 38 areprovided in the coupling 30 and closed by threaded plugs 40 to provide anumber of relatively shallow recesses 42 in the inner wall of thecoupling 30, such recesses being radially alignable with theircorresponding apertures 36 in the mandrel.

Positioned in and substantially filling each corresponding pair ofapertures 36 and recesses 42 is a ball detent 44 which serves to lockthe mandrel 1t) and the sleeve 16 against relative axial movement. Atubular member 46 projects upwardly from the cutter head 32 into thelower end of the mandrel 10 and engages the inner sides of all of theball detents 44 to retain the latter within the aper tures 36 andrecesses 42 and thereby maintain the sleeve f 16 and mandrel 10 lockedagainst relative axial movement. It will be seen, however, that when thetubular element 46 is removed, the ball detents 44 may escape from theirrespective apertures and recesses and thereby permit relative axialmovement between the mandrel and the sleeve. The means for effectingremoval of the tubular detent-retaining member 46 will be describedlater.

The cutter head 32 comprises a tubular member 48 having a plurality(five as shown in the drawings) of and carrying the blade by means of anelongated bearing aperture 56 in the latter. Such bearing aperture 56 iselongated in a direction substantially normal to the mill ing edge 58 ofthe blades 52, for reasons later described. The interior of the upperportion of the cutter head 32. forms a cylinder 60 in which a tubularpiston 62 is mounted for reciprocation axially of the cutter head. Thepiston 62 is spring-biased into an upward position by means of a coilspring 64 disposed between a reduced portion 66 of the piston and thecylinder wall 64 and bearing against the underside of the piston head 68and an abutment ring 70 seated on a shoulder 72 formed in the bore ofthe cutter head below the cylinder 60. The reduced portion 66 of thepiston extends downwardly and has a plurality of radial apertures 74which somewhat loosely receive the inwardly-extending tapered operatingtongues 76 of the cutter blades 52. Y

From this construction it will be seen that when the piston 62 is in theposition shown in Figure 2B, the cutter blades are retracted within theslots, but that when the piston moves downwardly, under the influence offluid pressure from the drill string 12 as later described, the cuttersare pivoted about the pins 54 so that their outer severing edges 78 moveoutwardly into engagement with the inner wall of the casing 80. Rotationof the drill string 12 then serves to cut a groove in the inner wall ofand subsequently to sever the casing 80. After the casing has beensevered, the cutters 52 are moved further outwardly, by the piston 62,until their milling edges 58 are in milling engagement with the end 82of the severed casing 80, as shown in Figure 3. The piston 62 is stoppedat the end of its cutter projecting movement by engagement of its head68 with a shoulder 84 formed in the cutter head bore at the lower end ofthe cylinder 6th. In this position of the piston the cutter tongues 76are free ofengagement with the upper and lower sides of the apertures74, but instead engage with the upper edge of an annular guide ring 86for the reduced lower end 88 of the operating extension 66 of the piston62. In this position of the cutters, the elongated bearing slot 56renders the pivot pins 54 inoperative so that the cutters 52 arefulcrumed about the upper edge of the annular guide ring 86.

At the upper end of each slot 50, the cutter head 32 is provided with alongitudinal bore 90 in which is mounted a spring 92 bearing against thebase of the bore 90 and a follower 94 that is engaged with the back ofeach cutter blade 52. The followers 94 are retained within the bores 90by means of transverse retaining pins 96 passing through elongatedopenings in the followers and having their ends anchored in the boreside walls, shown best in Figure 3. The action of the springs 92 is tohold each cutter blade 52 against the end edge 82 of the casing so thatall of the cutters are simultaneously, and uniformly, effective in theirmilling action. It will be seen that by fulcruming the cutter blades 52on the guide ring 36, instead of on their pivot pins 54, an increasedmechanical advantage is obtained. As a result of this construction anincreased milling rate, from three to five times greater thanconventional casing mills, is obtained.

The tubular detent retaining member 46 extends through a central sleeve98 of a spider-like guide ele ment 10d, threaded into the lower end ofthe coupling 30, and is threaded into the upper end of the piston 62.The length of the detent retaining member 46 is so proportioned thatwhen the piston 62 has moved downwardly into position to project thecutter blades 52 into their milling position, the upper end of themember 46 clears the ball detents 44 sufficiently to permit the latterto drop, or be forced out of, their corresponding apertures 36 andrecesses 42 and fall into a cup-like upper enlarged portion 102 of thebore through the retaining member. Thus the sleeve 16 and mandrel 10 arereleased for relative axial movement.

The cutter blade projecting movement of the piston 62 is effected bymeans of fluid pressure from the drill string 12 which passes betweenthe mandrel 10 and detent-retaining member 46, through the guide element100, and into the cylinder 60 to act on the upper surface of the piston62. In this connection it will be noted that although the fluid pressuremay also pass through the bore of the tubular detent-retaining member 46and through the bore of the tubular piston 62 for escape outwardlythrough the apertures 74 and slots 50 to both lubricate the cutters 52and carry away cuttings, the bore of the detent retaining member has asomewhat restricted throat portion 104 so that sufiicient fluid pressuremay be built up within the cylinder 60 to force the piston 62downwardly. It also will be noted that even though the bore of themember 46 may be closed by the seating of a detent ball 44 against theupper end of the throat portion 104, as shown in Figure 3, lateral ports106 are provided in the detent-retaining member, that are normallyclosed by the sleeve 98 of the spiderlike guiding element 100. In theposition of the parts shown in Figure .3, however, these ports 1% areuncovered to permit drill fluid to pass inwardly therethrough andcontinue to flow downwardly through the tubular piston 62 in order toprovide the aforementioned lubricating and cuttings disposal action.

In operation, the apparatus is connected to a drill string 12 and runinto a cased bore hole to the desired depth. Fluid pressure is thenapplied through the string 12 to force the piston 62 down and move thecutter blades 52 into severing engagement with the casing 80. Rotationof the string 12 then serves to sever the casing 80 at the selecteddepth, whereupon the cutter blades 52 move through the resulting annularaperture and into milling engagement with a severed end 82.Simultaneously the mandrel 10 and sleeve 16 are unlocked by the releaseofthe ball detents 44. Continued rotation of the string 12 then servesto rotate the cutters 52 against the casing edge 82 to mill away thesame, while fluid pressure from the drill string acts against the piston62 and the annular enlargement 22 on the mandrel to effect axialmovement between the sleeve 16 and the mandrel and to thereby move thecutter head 32 downwardly to maintain the cutter blades 52 in engagementwith the edge 82 of the casing section being milled away. Of course, thefluid pressure necessary to accomplish such downward movement of thecutter head has an equal and opposite reaction tending to cause upwardmovement of the drill string. Since the latter is of great weight,however, such fluid pressure is insuflicient to raise the same andinstead, the cutter head is moved downwardly. The pressure with whichthe blades 52 bear against the casing 80 is accurately controlled fromthe surface by controlling the fluid pressure in the string 12.Obviously, the mandrel 10 and sleeve 16 may be made as long as practicalfor milling away casing sections of any desired length.

After the casing section has been removed, the drill string pressure isreduced to permit retraction of the cutter blades 52 by upward movementof the piston 62 by the spring 64. The string and tool are thenwithdrawn from the well. in the event the blades 52 stick in theirprojected position or the spring is not strong enough to retract them,the backs of the blades will engage the edge 63 of the severed casing,upon withdrawal of the string, and be deflected thereby back into theirslots :"ill.

The cutter head 32 preferably is provided with a depending reducedtubular extension 168 on which is rotatably mounted, by means ofanti-friction bearing assemblies lid, an eccentric guiding assembly 112.This assembly 112 is provided with a circumferential series of 3longitudinally extending ribs 114, the outer surfaces of which lie incylindrical surface that is eccentric with respect to the axis of thecutter head 32. The guiding assembly 112 is held in place by means of anut 116 that is locked in position by a ball detent 118 received inradially aligned grooves 120 and 122 in the outer surface of theextension and the inner surface of the nut, respectively. The balldetent 118 may be held in place by a conical ribbed guiding cap 124threaded onto the lower end of the cutter head extension 108. Inoperation, the ribs .114 of the guiding assembly 112 engage the innerwall of the casing 80, as shown in Figure 1, and serve to maintain thecutter head 32 in position to rotate about an axis that is off-centerwith respect to the axis of the casing =30, to thereby achieve, ineifect,

a simultaneously reciprocating and rotating movement of the blades 52 inorder to effectively utilize their entire milling edge and preventgrooving of the same. The eccentric guiding assembly 112 and itsfunction are described more fully in detail in the copending applicationof Earl .l. Robishaw, Serial No. 157,533, filed April 22, 1950, now latent No. 2,690,217. Also, a considerable portion of the drilling fluidescapes, via the extension Mid, into the casing below the tool. Thisfluid returns to the surface upwardly between the tool and the casing toaid in the cuttings disposal.

will thus be seen that the purposes of this invention have beenelfectively accomplished. It will be realized, however, that thespecific embodiment of a casing mill, used to illustrate the principlesof this invention, may be changed without departing from the principlesof the invention. Therefore, this invention includes all modificationswhich are encompassed by the spirit and scope of the following claims.

We claim:

1. A tool for severing the casing of a cased bore hole and milling awaya section thereof comprising: a cutter head; means for connecting saidhead to a drill string for rotation therewith and for axial movementrelative thereto; means for locking said connecting means against saidaxial movement; at least one cutter mounted on said head for outwardradial movement into severing and subsequent milling engagement with thecasing; means for moving said cutter outwardly; and means operable bysaid cutter moving means for unlocking said locking means upon severanceof the casing and movement of said cutter into milling engagement with asevered end thereof.

2. A tool for severing the casing of a cased bore hole and milling awaya section thereof comprising: a cutter head; means for connecting saidhead to a drill string for rotation therewith and for axial movementrelative thereto, said connecting means including means operable bydrill string fluid pressure for forcefully effecting said axialmovement; means for locking said connecting means against said axialmovement; at least one cutter mounted on said head for outward radialmovement into severing and subsequent milling engagement with thecasing; means operable by drill string fluid pressure for effecting saidradial cutter movement; and means operable by said last-mentioned fluidpressure means for unlocking said "locking means upon severance of thecasing and movement of said cutter into milling engagement with asevered end thereof.

3. The structure defined in claim 2 including resilient means urging thecutter for inward radial movement.

4. A tool for severing the casing of a cased bore hole and milling awaya section thereof comprising: a cutter head; splined means forconnecting said head to a drill string for rotation therewith and axialmovement relative thereto, said connecting means including a fluidpassageway therethrough to communicate with the drill string forforcefully effecting said axial movement: by application of fluidpressure through the drill string; means for locking said connectingmeans against said axial movement including at least one detentpositionable in radially aligned apertures in relatively movableelements of said splined means; at least one cutter mounted on said headfor outward radial movement into severing and subsequent millingengagement with the casing; movable means in said head engageable withsaid cutter and operable by drill string fluid pressure for elfectingsaid outward cutter movement; and retaining means carried by said cuttermoving means and engageable with said detent for retaining the latter insaid apertures until said cutter has severed the casing and moved intomilling engagement with a severed end thereof.

5. A tool for severing the casing of a cased bore hole and milling awaya section thereof comprising: a cutter head having a cylindertherewithin and. at least one cutter mounted thereon for outward radialmovement into severing and subsequent milling engagement with thecasing; spring-biased piston means within said cylinder and engageablewith said cutter for effecting said outward movement; a tubular mandrelconnectable to a drill string; a sleeve sealingly splined to saidmandrel. and carrying said cutter head for rotary movement with thedrill string and axial movement relative thereto, said sleeve andmandrel serving to conduct fluid from the string to said cylinder; meansfor locking said mandrel and said sleeve in their fully telescopedposition against relative axial movement, said locking means includingat least one radial aperture in said mandrel alignable with a shallowrecess in the inner wall of said sleeve and a ball detent substantiallyfilling said aperture and recess; and rod-like means secured to saidpiston means and extending into said mandrel in position to engage andretain said ball detent in looking position, said rod-like 11 cans beingdisengaged from said detent to release the latter for movement fromlocking position upon movement of said piston means into position foreffecting milling engagement of said cutter with the casing, whereuponrelative axial movement between said cutter head and the drill stringmay be effected by drill string fluid pressure to move the cutteragainst the casing during the milling operation.

6. In a tool rotatable by a drill string for severing the casing of acased bore hole and milling away a section thereof, and having a cutterhead, a plurality of cutters pivotally carried by said head for outwardprojection into cutting relation with the casing to first sever the sameand then mill away a section thereof by axial movmeent of the head, thecombination of spring means carried by the head and engaging the back ofeach said cutter at a longitudinal location between its pivotal mountingand its effective milling edge to individually maintain each said cutterin milling engagement with the end of the severed casing.

7. A tool rotatable by a drill string for severing the casing of a casedbore hole and milling away a section thereof, said tool comprising: acutter head connectable to a drill string for rotation therewith; aplurality of cut ters pivotally mounted in said head for radial outwardmovement into cutting engagement with the casing, each said mountingcomprising a pivot pin passing through an elongated bearing opening inthe corresponding cutter, the direction of elongation of said openingbeing normal to the milling edge of the cutter; fluid-pressure-operablemeans within said head engageable with the inner ends of said cutters toeffect said outward movement; abutment means on said head engageable bysaid inner ends at the end of their pivotal movement and constituting afulcrum point therefor; and a spring interposed between said head andthe back of each said cutter at a location between the ends thereof forindividually maintaining each cutter in milling engagement with the endof the casing after severance thereof.

8. Apparatus for severing the casing of a cased bore hole and millingaway a section thereof comprising: an operating string having upper andlower sections; means for connecting said lower section to said uppersection for rotation therewith and for axial movement relative thereto;a cutter head carried by said lower section; at least one cutter mountedon said head for outward projection into severing and subsequent millingengagement with the casing; means for projecting said cutter; means forlocking said connecting means against said axial movement while severingthe casing; and means for automatically unlocking said locking means assaid cutter moves into milling position after the casing has beensevered to release said operating string lower section for movement ofsaid cutter head carried thereby longitudinaily of the casing whilemilling the latter.

9. Apparatus for severing the casing of a cased bore hole and millingaway a section thereof comprising: a tubular operating string havingupper and lower sections; means for connecting said lower section tosaid upper section for rotation therewith and for axial movementrelative thereto, said connecting means including means operable byfluid pressure for forcefully effecting said axial movement; a cutterhead carried by said lower section; at least one cutter mounted on saidhead for outward projection into severing and subsequent millingengagement with the casing; means for projecting said cutter; means forlocking said connecting means against said axial movement while severingthe casing; and means 'for automatically unlocking said locking meanswhen said cutter moves into milling position after the casing has beensevered to release said operating string lower section for axialmovement by said fluid pressure means to move said cutter headlongitudinally of the casing while milling the latter.

10. Apparatus for severing the casing of a cased bore hole and millingaway a section thereof comprising: a

ment relative thereto; a cutter head carried by said lower section; atleast one cutter mounted on said head for outward projection intosevering and subsequent milling engagement with the casing; meansoperable by fluid pressure for effecting said cutter projection; meansfor locking said connecting means against said axial movement whilesevering the casing; and means operable by said fluid-pressure means forunlocking said locking means after the casing has been severed torelease said lower section for movement of said cutter head carriedthereby longitudinally of the casing while severing the latter.

ll. In a milling tool for operation against the end of a tubular casingand having a cutter head provided with a circumferential series ofcutters extending generally radially thereof and having cutting edgesfacing generally longitudinally of the tool for substantiallysimultaneous engagement with the casing end, the combination of meansmounting each cutter on the head for independent movement relativethereto in directions extending generally longitudinally thereof, andresilient means interposed between each of the cutters and a separatepart of the head for individually yieldingly limiting said relativemovement of each cutter in a direction opposite that faced by itscutting edge in order to individually maintain the cutters in engagementwith the work.

12. The structure defined in claim 11 in which the resilient meanscomprises a spring.

13. In a tool rotatable by a drill string for severing the casing of acased bore hole and milling away a section thereof, and having a cutterhead carrying a plurality of cutters mounted for generally radialoutward projection into cutting relation with the casing, the cuttershaving end cutting edges to first sever the casing and intermediatecutting edges substantially simultaneously engageable, by additionaloutward projection, with the severed end edge of: the casing to millaway a section thereof by axial movement of the head, the combination ofmeans mounting each cutter on the head for generally longitudinalindependent movement relative thereto when in milling position, andresilient means mounted on the head and engaged with each cutter forindividually urging the latter in the direction faced by itsintermediate cutting edge to maintain each cutter in milling engagementwith the sevcred casing end.

14. In a milling tool for operation against the end of a tubular casingto mill away a section thereof and carrying a circumferential series ofcutters, having cutting edges facing generally longitudinally of thetool and adapted to bear substantially simultaneously against the casingend edge, the combination of means mounting each cutter on the tool forindividual movement generally longitudinally of the tool, and meansmounted on the tool and bearing against each cutter for yieldablyresisting movement thereof in a direction opposite that faced by itscutting edge, as ur ed by the longitudinal reaction force on each cuttercaused by longitudinal movement of the tool against the casingend, inorder to maintain the cutters in cutting engagement with the casing endedge.

References Cited in the file of this patent UNITED STATES PATENTS1,094,169 Schoenborn Apr. 21, 1914 2,199,020 Y Barrett et al. Apr. 30,1940 2,299,528 Conner Oct. 20, 1942 2,322,694 Kinzbach a- June 22, 19432,394,236 Eastman Feb. 5, 1946 2,552,543 Earle et al. May 15, 1951

